Optical resolution of scanners and other image capture devices is continually being increased. Increasing the optical resolution allows more information to be captured. However, an increase in perceived noise can result.
Knowledge of noise levels can be useful in digital image processing. For instance, some denoising algorithms use a noise level estimate to adjust the aggressiveness of noise removal. If an estimate is too low, much noise will remain in the denoised image. If an estimate is too high, image features will be removed from the denoised image. Accurate noise estimation will produce better results.
Therefore, accurate noise level estimation is desirable. A noise level estimation that varies spatially is also desirable, especially for natural images and other images in which the perceived noise levels might be non-uniform.